Quote...and are put forward with an air of total certainty, without a shred of solid empirical evidence behind them? And how can this be done without any hesitation, shame or remorse?
To be fair, we do it too

We have no solid, scientifically accepted evidence that TSism is anything more than an odd psychological quirk. We ASSUME it's biological somehow, but we really don't know. The "incomplete hormonal bath when in the womb" theory is always mentioned as if it's accepted fact, when it's really just a good guess. Nor does it explain f2ms very well.
But just as the bigots have an agenda to invalidate our condition, it often seems we have a need to justify it.